Copolymers of vinyl chloride with fumaric acid esters, maleic acid esters, itaconic acid esters, acrylic acid esters, methacrylic acid esters, vinyl esters and vinyl ethers with saturated an unsaturated alkyl radicals are known. See, for example, H. Kainer 1965, pp.89-109 and Belgian Pat. No. 724,889.
It is furthermore known that an increasing internal plasticization is associated with an increase in the content of these comonomers in the copolymer, especially when they bear long alkyl chains; see, for example, W. S. Port et al., Ind. Eng. Chem 1955, p. 472. It is furthermore known that, if the external or internal plasticization is sufficiently high, copolymers of vinyl chloride display elastic properties; see, for example, German Offenlegungschrift No. 1,902,455. Products made from elastic copolymers of vinyl chloride, however, have the decided disadvantage that, as the content of external or internal plasticizer increases, tenacity decreases drastically, and solubility or swelling in many organic solvents increases.
These disadvantages render the products unusable for many applications in which high tenacity combined with high elongation is expected, or resistance to oils, gasoline or solvents is required. The cross-linking of vinyl polymers, where the cross-linking densities are low, has resulted in naught but a diminution of these disadvantages. Attempts have been made to increase the cross-linking density by adding additional polymers containing unsaturated groups, for example, polymers of diolefins, but this has necessarily resulted in a reduction of the percentage of the longer chain alkyl groups which bring about the internal plasticization.